1. Field of the Invention
The present invention relates to a recording/reproducing apparatus for dynamic image data such as HDTV and NTSC, and static image data such as SV. Particularly, the invention relates to a driving method for recording probe electrode for a miniaturized high density recording/reproducing apparatus which utilizes the principle of STM.
2. Related Background Art
Along the evolution of the laser technology in recent years, inexpensive high density recording media have been developed with the optical memory which uses an organic dye, photopolymer, or other organic thin film.
On the other hand, the scanning type tunnel microscope (hereinafter referred to as STM) has been developed recently, which makes possible direct observations of the electronic structure of surface atoms of conductors [G. Binning et al. Phys. Rev. Lett, 49, 57 (1982)]. As a result, the high resolution measurement of a real spatial image can be performed irrespective of whether it is monocrystalline or amorphous. There are still more advantages that the observation is possible with a low voltage without causing any damage to a specimen due to the running current while the operation can be executed in the atmosphere for various materials. Therefore, its wide range applications are expected.
The STM utilizes the tunnel current which flows between a probe electrode and a conductive substance when they approach each other as close as approximately 1 nm while a voltage is being applied. This tunnel current is quite sensitive to the variations of distance between them, and it is possible to read various pieces of information about the entire electronic clouds in a real space by scanning the probe electrode so that the tunnel current is kept constant. In this case, the resolution in the in-plane direction is approximately 0.1 nm.
With the utilization of the STM principle, therefore, a high density recording and reproducing can be performed satisfactorily with atomic order (sub-nanometers). For example, in a recording and reproducing apparatus disclosed in Japanese Patent Laid-Open Application No. 61-80536, the atomic particles adsorbed on the surface of medium are removed by an electron beam or the like to perform writing, and the data is reproduced by STM.
There is disclosed in Japanese Patent Laid-Open Application No. 63-161552 and No. 63-161553, a method for performing the recording and reproducing by the STM using a material having memory effect as a recording layer such as a .pi. electronic organic compound or a thin film of chalcogens compound for the switching characteristics of voltage current. According to this method, recording and reproducing with mass-memory as many as 10.sup.12 bits/cm.sup.2 are possible assuming that the recording bit size is 10 nm.
Now, in order to practice this method as an actual apparatus to perform recording to and reproducing from a memory medium, it is necessary to maintain the space between the recording layer and the probe electrode at a distance where the tunnel current flows as well as to allow the probe electrode to scan along the tracking groove of the recording layer.
Conventionally, as a scanning method for the probe electrode, there is disclosed a method in Japanese Patent Laid-Open Application No. 1-151035 and No. 1-107341 in which a spiral groove is formed on the recording medium surface on a disc in the same manner as applied to a video disc or the like, and the recording and reproducing are performed as if the probe electrode follows this groove.
It is a suitable method that image data is recorded on a disc type recording medium because image data is continuous and so-called sequential recording and reproducing are mainly required.
When a recording/reproducing apparatus using this STM principle is used as an image data memory, the size of a recording medium needed to satisfy the recording volume of 10.sup.12 bits, which is required for recording HDTV image data for one to two hours, is only 1 cm.sup.2. However, it is extremely difficult to control the distance between the recording layer and the probe electrode to be kept within a range (usually, 1 nm or less) for flow of the tunnel current while such a small recording medium is rotated at a high speed.
On the other hand, with a method for performing the recording with the probe which scans the recording medium surface in the x-y directions two dimensionally, it is relatively easy to control the distance between the probe electrode and the recording layer as compared with the above-mentioned example. However, since there is a problem that no recording and reproducing are possible at the returning point of the probe scanning, in this method it is difficult to handle any continuous signal such as an image signal.